Optical switch and method for aligning optical switch components

ABSTRACT

An optical switch having a fiber/lens array and a switching substrate may be properly aligned using one or more grating(s) provided on the switching substrate. The grating(s) may be designed to have a predetermined response when the fiber/lens array and switching substrate are properly aligned. For example, the grating(s) may reflect incident light back into an input fiber, where the back-reflected light may be detected. Accordingly, the position of the switching substrate and/or fiber/lens array may be adjusted until back reflected light having predetermined power is detected.

RELATED APPLICATIONS

This application is related in subject matter to U.S. application Ser.No. 09/754,254, filed concurrently herewith and expressly incorporatedby reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to an optical switch and a method foraligning components of an optical switch.

Increasing demands for high-speed Internet service and wirelesscommunications are soon expected to outstrip current telecommunicationscapacity. Because optical fiber networks are capable of transmittinghuge volumes of data at blinding speeds, telecommunications carriers areturning to optical fiber networks in an effort to meet future needs.

In order to implement optical fiber networks of the future, thetelecommunications industry needs new optical devices that areinexpensive, efficient, and scalable to accommodate future opticaltelecommunications network expansion. Telecommunications providersprefer optical fiber networks that can be reconfigured quickly andefficiently. This gives the optical network the flexibility toaccommodate growth and changes in future communications patterns. Theability to reconfigure quickly and efficiently also enables the networkto restore failed communications by rerouting the communications tobypass the failure.

Optical fiber networks can be reconfigured at network nodes usingoptical switches to change the coupling between incoming optical fibersand outgoing optical fibers. Currently under development are opticalswitches that use movable micro-mirrors. These optical switches couplethe optical signals between input and output fibers entirely in opticalform, instead of converting the optical signals to electrical signals,switching the electrical signals, and converting the switched electricalsignals back to optical signals.

To successfully operate such switches, the switch components—includingfibers, lenses, and the micro-mirrors—must be properly aligned and theangular position of the movable micro-mirrors must be preciselycontrolled. If the components are not properly aligned, some or all ofthe light from the input fibers will not reach the selected outputfiber. There remains a need in the art for an optical switch havingcomponents that may be easily and accurately aligned and a method foraligning the switch components.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstancesand has as an object to provide an economical optical switch havingcomponents that may be easily aligned.

A further object of the invention is to provide a method for aligningcomponents of an optical switch.

Additional objects and advantages of the invention will be set forth inpart in the description that follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention will be realized and attained bymeans of the elements and combinations particularly pointed out in theappended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiment(s) of the inventionand together with the description, serve to explain the principles ofthe invention.

FIG. 1 provides a schematic of an illustrative optical network inaccordance with the present invention.

FIG. 2 provides a schematic of an exemplary optical switch in accordancewith the present invention.

FIG. 3 illustrates an embodiment of an exemplary optical switch havingmicro-mirrors in accordance with the present invention.

FIG. 4 illustrates the alignment of components of the exemplary opticalswitch shown in FIG. 3 in accordance with the present invention.

FIG. 5 illustrates an exemplary embodiment of a MEMS array substrate ofan optical switch in accordance with the present invention.

FIG. 6 illustrates a partial cross-section of the embodiment of the MEMSarray substrate of FIG. 5.

FIG. 7 illustrates a partial top view of an exemplary sub-mount of theMEMS array substrate of FIG. 5.

FIG. 8 illustrates a cross-sectional view of a planar grating inaccordance with the present invention.

FIG. 9 illustrates a schematic of a first exemplary optical detector inaccordance with the present invention.

FIG. 10 illustrates a schematic of a second exemplary optical detectorin accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the present exemplaryembodiment(s) of the invention illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

The present invention is useful in optical switches for opticaltelecommunications network systems that carry optical communicationssignals, such as wavelength division multiplexed (WDM) signals, overoptical fibers. FIG. 1 illustrates an exemplary embodiment of an opticalmesh communications network 1. While FIG. 1 illustrates an optical meshnetwork, the present invention may be used in connection with otheroptical network architectures, such as ring, chains, and stars, amongothers, as well as other optical applications. As shown, the network 1includes optical network elements 2-1 to 2-8 interconnected throughoptical links 3 in a mesh pattern. Of course, the number of opticalnetwork elements 2 and interconnections shown in FIG. 1 is intended asan example only. It should be clear that the present invention isapplicable with different numbers and/or interconnections of networkelements 2. The optical links 3 are shown generally and may encompassdifferent numbers of optical paths and different physical paths betweenthe network elements 2. The optical links 3 may include, for example,optical fiber.

In general, the optical network elements 2 communicate informationsignals to other optical network elements through the optical links 3.The optical network elements 2 may include optical cross-connects,add-drop multiplexers, or other switching equipment to allow the signalscarried on the optical links 3 to be transmitted through the networkelements 2, as necessary, from source to destination. In addition, andnot shown in FIG. 1, the optical network elements 2 may be connected toinformation sources (ingresses) and destinations (egresses) in thelocality of that optical network element 2. Thus, for example,information signals may enter the optical mesh network 1 at a localconnection to network element 2-1. The information signals may beconverted to optical signals, if they are not already, and then travelin the optical network 1 from network element 2-1, through networkelements 2-4 and 2-6, and to network element 2-8, where it is passed toa destination in the locality of network element 2-8.

FIG. 2 illustrates a schematic of such an exemplary optical switch 10 inaccordance with the present invention. Optical switch 10 may be locatedin an optical network element 2, such as shown in FIG. 1. The opticalswitch 10 according to the present invention may be configured as anoptical cross connect (OXC), an add-drop multiplexer (ADM), or anotheroptical switch arrangement.

The optical switch 10 switches optical signals from a plurality of inputoptical fibers 20-1 to 20-j (collectively “input optical fibers 20”) toselected output fibers 25-1 to 25-j (collectively “output optical fibers25”). The optical signals may be provided, for example, from a localingress or from another node 2 and may be selectively provided to aselected node 2 or local egress. The present invention is not limited bythe types of the optical signals carried by the input optical fibers 20and output optical fibers 25. Each optical input fiber 20 may carry WDMsignals, a single wavelength optical signal that was demultiplexed froma WDM signal by a wavelength division demultiplexer, or other types ofoptical signals. Similarly, each optical output fiber 25 may carry WDMsignals, single wavelength optical signal to be multiplexed with otheroptical signals by a wavelength division multiplexer, or other types ofoptical signals. The optical signals typically carry information and mayhave wavelengths of about 1300-1500 nm, for example. While FIG. 2 showsa schematic of an embodiment with j input optical fibers 20 and j outputoptical fibers 25, the number of input optical fibers 20 may differ fromthe number of output optical fibers 25.

Optical switch 10 may further include input optical fibers 22-1 to 22-N(collectively “input optical fibers 22”) and one or more output opticalfibers 27-1 to 27-N (collectively “output optical fibers 27”). Thenumber of input optical fibers 22 and the number of output opticalfibers 27 may differ, of course. Input optical fibers 22 and outputoptical fibers 27 may be used for alignment purposes, as discussedfurther below. In the embodiment shown in FIG. 2, fibers 22 and 27 arecoupled to light source 34 and to detectors 33, as shown schematicallyin FIG. 2. Light source 34 launches optical signals into fibers 22 and27. Light source 34 may be for example, a light-emitting diode, a laser,or other light source, or a group of such devices provided for fibers 22and 27. For example, one or more fibers 22, 27 may be coupled to eachsuch device. Detectors 33 detect optical signals propagating in fibers22 and 27 in a direction opposite to the optical signals output fromlight source 34.

The input optical fibers 20, 22 and output optical fibers 25, 27 may bearranged in any way, for example a rectangular array, such as a squarearray. Alternatively, input optical fibers 22 may be provided outside ofor interspersed within an array of fibers 20. Similarly, output fibers27 may be provided outside of or interspersed within an array of fibers25. In an exemplary embodiment, fibers 22 and 27 are provided at theperiphery of the arrangement of fibers.

The input optical fibers 20, 22 carry optical signals that are supplied,respectively, to a lens array 30. The lens array 30 may include aplurality of micro-lenses 32 arranged in an array. The micro-lenses 32are preferably arranged so that each input optical fiber 20 and 22 isaligned with a micro-lens 32. In this way, optical signals emitted froman input fiber 20, 22 will pass through one of the micro-lenses 32.Alternatively, the lens array 30 may be integrated with the ends offibers 20, 22. The input fibers 20, 22 and lens array 30 maycollectively be considered a fiber/lens array. The micro-lenses 32direct optical beams from the input optical fibers 20 to a firstswitching substrate 100 a, which will be described in greater detailbelow.

The first switching substrate 100 a includes a plurality of gratings 111a-1 to 111 a-N (collectively referred to as “gratings 111 a”) and aplurality of switching elements 120. The switching elements 120 may bearranged in an array, e.g., a rectangular or square array. Gratings 111a may be arranged at the periphery of the array of switching elements120 or interspersed within the array of switching elements 120.Alternatively, the gratings 111 a and switching elements 120 maytogether form an array, e.g., a rectangular or square array. Of course,other arrangements of the gratings 111 a and/or switching elements 120may be used as well.

According to one embodiment of the invention, the gratings 111 areplanar reflective or blazed gratings. Gratings 111 a are located on theswitching substrate 100 a so that, when fiber/lens array 20,22/30 andswitching substrate 100 a are properly aligned, optical signals frominput optical fibers 22 pass through lenses 32, strike gratings 111 a,at least a portion of the incident optical signals are reflected backthrough lenses 32 and into fibers 22, and are detected by detectors 33.If the switching substrate 100 a and fiber/lens array 20,22/30 aremisaligned, light from at least one fiber 22 and emitted from a lens 32will not be reflected back into the fiber 22 by grating 111 a.Accordingly, detectors 33 will not detect back-reflected light fromgratings 111 a in each of the fibers 22.

The switching elements 120 of switching substrate 100 a may include, forexample, micro-mirrors. In a preferred embodiment, each input opticalfiber 20 corresponds to one micro-lens 32 of the first lens array 30 andone micro-mirror switching element 120 of the first switching substrate100 a. Using the switching elements 120 and responsive to controlsignals, the first switching substrate 100 a couples the optical signalsfrom the fibers 20 to selected switching elements 120 of a secondswitching substrate 100 b.

The second switching substrate 100 b includes gratings 111 b-1 to 111b-N (collectively “gratings 111 b”) and switching elements 120. Similarto the first substrate 100 a, the switching elements 120 of the secondsubstrate 100 b may be arranged in an array, e.g., a square orrectangular array or other arrangement. Gratings 111 b may be arrangedat the periphery of the substrate 100 b or interspersed therein.Alternatively, the gratings 111 b and switching elements 120 maytogether form an array, such as a rectangular array. As above, thegratings 111 and switching elements 120 may form other patterns onsubstrate 100 b. The second substrate 100 b need not match the firstsubstrate 100 a.

Gratings 111 b may be, for example, planar reflective or blazedgratings. Gratings 111 b are located on the switching substrate 100 b sothat, when fiber/lens array 25,27/35 and switching substrate 100 b areproperly aligned, optical signals from output optical fibers 27 passthrough lenses 32, strike gratings 111 b, at least a portion of theincident optical signals are reflected back through lenses 32 and intofibers 27, and are detected by detectors 33. If the switching substrate100 b and fiber/lens array 25,27/35 are misaligned, light from at leastone fiber 27 and emitted from a lens 32 will not be reflected back intothe fiber 27 by a grating 111 b. Accordingly, detectors 33 will notdetect back-reflected light from gratings 111 b in each of the fibers27.

Switching elements 120 of substrate 100 b may include, for example,micro-mirrors. In a preferred embodiment, each output optical fiber 25corresponds to one micro-lens 32 of the second lens array 35 and onemicro-mirror switching element 120 of the second switching substrate 100b. Using the micro-mirror switching elements 120 and responsive tocontrol signals, the second switching substrate 100 b couples opticalsignals from the first switching substrate 100 a to output fibers 25.

In one embodiment, each switching element 120 of the first substrate 100a is preferably movable or otherwise controllable to permit an inputbeam to be coupled (e.g., reflected) by the switching element 120 to anyswitching element 120 of the second substrate 100 b. The switchingelements 120 of the second substrate 100 b, also responsive to controlsignals, receive and couple the optical beams through the second lensarray 35 to output optical fibers 25. The fibers 20, 22 and lens array30 may collectively be considered as a fiber/lens array. The second lensarray 35 includes micro-lenses 32, which may be arranged in an array,aligned with output optical fibers 25 and 27. Alternatively, lenses 32may be integrated with the ends of fibers 25 and 27. Micro-lenses 32direct the optical beams into output optical fibers 25 and into and outof fibers 27. Accordingly, optical signals carried on input opticalfibers 20 may be selectively coupled to output optical fibers 25.

A controller 50 may be used to receive and process sensor signals (e.g.,from the detectors 33 and/or from the switching substrates 100 a, 100 b)and other control inputs and generate output control signals to controlthe position of the switching elements 120 of the first and secondsubstrates 100 a, 100 b. The switching substrates 100 a and 100 b can becontrolled to redirect or switch the coupling of optical signals. Forexample, as shown in FIG. 2, switching element 120-1 of substrate 100 adirects an optical signal to switching element 120-(k+1) of substrate100 b. However, responsive to control signals, switching element 120-1of substrate 100 a may redirect the optical signal it receives frominput optical fiber 20-1 to switching element 120-2 of substrate 100 b.Switching element 120-2 may be controlled to receive the optical signaland provide it to optical fiber 25-2. The controller 50 may be, forexample, a computer or application-specific circuitry.

Controller 50 may also generate control signals indicating whether ornot the fiber/lens array 20,22/30 is aligned with the first substrate100 a and whether the fiber/lens array 25,27/35 is aligned with thesecond substrate 100 b based on inputs received from detectors 33. Ofcourse, a separate controller may be used for this purpose. The controlsignals may be simply information signals indicating alignment ormisalignment. Alternatively, the control signals may indicate thedirection and displacement needed to bring the fiber/lens arrays20,22/30 and 25,27/35 into alignment with their respective substrates100 a, 100 b. A motor mechanism (not shown) may be provided for each ofthe first lens array/first switching substrate and the second lensarray/second switching substrate. The motor mechanism may be responsiveto the control signals of the controller 50 to move one or both the lensarray 30 (35) and substrate 100 a (100 b) into alignment. In this way,the combination of fiber/lens array/switching substrate may beautomatically aligned.

While FIG. 2 shows a one-stage switching arrangement, one or moreadditional stages of substrates may be interposed between substrates 100a and 100 b to form a multi-stage switching arrangement.

FIG. 3 provides an example of an embodiment of an optical switch 10according to the schematic of FIG. 2. As shown in FIG. 3, the inputoptical fibers 20 and 22 together form a two-dimensional rectangulararray. In particular, input optical fibers 22-1 to 22-4 are provided atthe corners of the array with input optical fibers 20 making up theremainder of the array. Of course, the arrangement of input opticalfibers 20 and 22 shown in FIG. 3 is exemplary and other patterns may beused consistent with the present invention. Similarly, output opticalfibers 25 and 27 together form a two-dimensional rectangular array inwhich fibers 27-1 to 27-4 are provided at the comers. Lens arrays 30 and35 include micro-lenses 32 arranged in arrays and desirably aligned withthe input optical fibers 20, 22 and the output optical fibers 25, 27,respectively.

Gratings 111 b and switching elements 120 of the second switchingsubstrate 100 b are arranged in a rectangular array, with the gratings111 b at the comers. Gratings 111 a and switching elements 120 aresimilarly situated on the first switching substrate 100 a. The switchingsubstrate 100 a is desirably positioned at an angle α1 with respect tolens array 30. That is, a ray taken normal from the surface of lensarray 30 will strike switching substrate 100 a at an angle α1 fromnormal. Switching substrate 100 a generally faces the second switchingsubstrate 100 b with some offset. The second switching substrate 100 bis desirably positioned at an angle α2 with respect to the second lensarray 35. In a preferred embodiment, α1 and α2 are equal. Accordingly,an optical path from an input fiber 20 to an output fiber 25 traverses agenerally “Z” shaped path, as illustrated in FIG. 3.

To position lens array 30 and switching substrate 100 a, an opticalsignal source 34, such as a light emitting diode, a laser, or othersignal source, is coupled to the ends of fibers 22. As noted above, asingle optical signal source 34 may be used to generate light for eachof fibers 22 or separate optical sources 34 may be used for each fiber22. The optical signals are emitted from the ends of fibers 22 andcollimated by micro-lenses 32. Lens array 30 and switching substrate 100a are moved relative to each other (e.g., by moving lens array 30,substrate 100 a or both) until the optical signals are reflected backinto the fibers 22 by gratings 111 a. The reflected light may bedetected by detectors 33. The lens array 30 and switching substrate 100a are properly aligned when detectors 33 detect-reflected signals ofpredetermined intensity or power from each of fibers 22-1 and 22-4. Thepredetermined power may be, for example, a maximum power determinedduring alignment or power that exceeds a predetermined threshold. Lensarray 35 and switching substrate 100 b may be aligned in a similarmanner.

Once properly aligned, the optical switch 10 may be used to selectivelycouple optical signals from input fibers 20 to selected output fibers25. As shown in FIG. 3 with a single optical beam, the first lens array30 receives the input optical beam from the input optical fibers 20 at amicro-lens 32 and directs the input beam to a switching element 120 ofthe first switching substrate 100 a. Depending on the angular positionof the switching element 120, the input optical beam is reflected to aselected switching element 120 of the second substrate 100 b. Theswitching element 120 of the second substrate 100 b reflects the inputoptical beam through a lens 32 of the second lens array 35 to a selectedone of the output optical fibers 25. Thus, the optical beam passes outof the input optical fiber 20, passes through a lens 32 of the firstlens array 30, is reflected by switching elements of the first andsecond switching substrates 100 a, 100 b, passes through a lens 32 ofthe second lens array 30, and is directed into a selected output opticalfiber 25.

In a preferred embodiment, switching substrates 100 a and 100 b aremicro-electromechanical system (MEMS) devices. Switching elements 120may be movable micro-mirrors. For example, switching elements 120 may begimbaled micro-mirrors capable of pivoting about at least two axes. Theaxes may be perpendicular to each other. Gratings 111 a and 111 b may beformed on the substrates 100 a, 100 b, respectively, using lithographicprocessing techniques used in the semiconductor arts. Alternatively,gratings may be formed separately and attached to the substrates.

FIG. 4 illustrates components of an exemplary optical switch 10 inaccordance with the present invention. In particular, FIG. 4 shows thejuxtaposition of the lens array 30 and the first switching substrate 100a. The arrangement of gratings 111 a and switching elements 120 on thefirst switching substrate 100 a is similar to that of FIG. 3, except thesubstrate 100 a includes more rows and columns of switching elements120. As can be appreciated from FIG. 4, the lens array 30 and theswitching substrate 100 a are canted with respect to each other.

FIGS. 5 and 6 illustrate a top view and a cross sectional view of anexemplary embodiment of a MEMS micro-mirror substrate 100 in accordancewith the present invention. In particular, FIG. 6 represents a partialcross section of the MEMS micro-mirror substrate 100 of FIG. 5 takenalong an axis A-A′. As should be apparent, FIGS. 5 and 6 providesimplified illustrations of MEMS micro-mirror substrate 100 forexplaining the invention. While FIGS. 5 and 6 described the switchingsubstrate 100 formed using MEMS technology, it should be appreciatedthat this is exemplary and other technologies may be used consistentwith the present invention.

The substrate 100 includes a base 110, which may be formed, for example,of single-crystalline silicon, on which a plurality of gratings 111 andmicro-mirrors 122 are formed in an array. More particularly, the base110 includes a plurality of micro-mirrors 122 and corresponding mirrormounts 124 for mounting the micro-mirrors 122. The micro-mirrors 122 maybe formed with a gold coating, for example, to provide a reflectivesurface. Each micro-mirror 122 and corresponding mirror mount 124 form amovable micro-mirror switching element 120. FIG. 5 shows four gratings111 and thirty-one movable micro-mirror switching elements 120 forpurposes of illustration. Of course, the switching substrate 100 mayhave more or fewer than four gratings 111 and/or more or fewer thanthirty-one movable micro-mirror switching elements 120.

As shown in FIG. 5, each mirror mount 124 may be formed as a gimbal. Inparticular, the mirror mount 124 includes a mounting arm 125 coupled tothe remainder of the base 110 by pivot arms 126-1, 126-2 and coupled tothe micro-mirror 122 by pivot arms 127-1, 127-2. Pivot arms 126-1 and126-2 enable the mounting arm 125, and thus the micro-mirror 122, topivot with respect to the substrate 110 about a first axis 126. Pivotarms 127-1 and 127-2 enable the micro-mirror 122 to pivot with respectto the mounting arm 125 about a second axis 127 orthogonal to the firstaxis 126. FIG. 5 shows the mounting arm 125 to be circular for purposesof illustration and not by way of limitation. Of course, the mountingarm 125 may be, for example, rectangular, elliptical, or other closedloop shape, or U-shaped, or arcuate.

The micro-mirror substrate 100 further includes a sub-mount 150 beneaththe base 110. The sub-mount 150 may be formed, for example, of siliconor another semiconductive material or compound, or an insulativematerial on which a semiconductive material or compound may be formed.FIG. 7 illustrates a top view of a portion of sub-mount 150 inaccordance with an exemplary embodiment of the invention. As shown inFIGS. 6 and 7, the sub-mount 150 includes a plurality of electrodes 170arranged in groups 170-1, 170-2 corresponding to the movablemicro-mirror assemblies 120-1, 120-2 and, in particular, to themicro-mirror 122-1, 122-2 and mounting arm 125 of the movablemicro-mirror switching elements 120. Group 170-1 and group 170-2represent two of several possible orientations of the electrodes 170relative to the axes 126 and 127. Of course, groups of electrodes 170 ofa given sub-mount 150 may have a single orientation or multipledifferent orientations. Electrodes 170 act on the micro-mirror 122 andmounting arm 125 to control the angular position of the micro-mirror 122by electrostatic force, for example. In the embodiment of FIGS. 5-7, theelectrodes 170 a and 170 c of electrode group 170-1 control the angularposition of the micro-mirror 122-1 about axis 127. Electrodes 170 b and170 d of group 170-1 control the angular position of the micro-mirror122-1 about axis 126. With respect to electrode group 170-2, electrodepairs 170 a, 170 d and electrode pairs 170 b, 170 c control the angularposition of the micro-mirror 122-2 about axis 126. Electrode pairs 170a, 170 b and electrode pairs 170 c, 170 d of group 170-2 control theangular position of the micro-mirror 122-2 about axis 127. Consequently,by appropriate control of electrodes 170 a-170 d, the surface angle ofmicro-mirror 122 may be controlled. Accordingly, the micro-mirror 122can be used to steer an incident light beam to a particular location, afunction useful in optical switches. The design of electrodes 170 inFIG. 7 is intended to be exemplary. It should be understood that otherelectrode designs may be used in connection with the present invention.

Control circuitry for driving the electrodes 170 may employ analogand/or digital designs. The control circuitry 50, or a portion thereof,may be integrated into the sub-mount 150 or may be provided by one ormore separate driver chips. Optical switch 10, and in particularsubstrates 100 a and 100 b and lens arrays 30 and 35 may includeadditional features to facilitate alignment and to facilitatepositioning control of the micro-mirrors 122.

FIG. 8 illustrates an exemplary grating 111 that may be in accordancewith the present invention. As noted above, grating 11 may be formed onthe surface of switching substrate 100 using, for example,photolithographic techniques or may be formed separately and bonded tothe surface of the substrate 100. The grating 111 may be formed bylinear grooves or by curved grooves, such as concentric circulargrooves, or by another configuration. As shown in FIG. 8, grating 111may be designed so that a first order component of light incident to thegrating at an angle α will be retro-reflected back at an angle α. Othercomponents of the incident light may be reflected at other angles. Ifthe grating 111 is designed so that α is the desired angle between thelens array and the switching substrate, grating 111 will reflect lightfrom the lens array directly back to the lens array at the same angle α.The retro-reflected light will be inserted back into the fiber 22 fordetection by detector 33. The output of detector 33 may therefore bemonitored to determine if the lens array and the switching substrate areoriented and aligned properly. The area of the grating may be smallerthan the cross-section of the optical beam, so that if there is anylateral misalignment between the grating and the Gaussian optical-beam,the output signal intensity of the detector 33 will decrease.

As an example, for a general grating without blazed angle, the firstorder component of light reflected by grating 111 will behave inaccordance with the following relationship:

2dsin α=λ  (1)

where α is the angle of incident light, α is the wavelength value of theincident light, and d is the groove spacing of the grating.

The angle of incidence of light from lens array 30 on substrate 100depends on the orientation of the lens array relative to the substrate100. The desired angle α between the substrate 100 and the lens array 30may be, for example, between 15°−30°, depending on the implementation.By way of example, if α is 20°, the groove spacing will be 1.9 μm forincident light of wavelength 1.3 μm and the groove spacing will be 2.19μm for incident light of 1.5 μm.

The size of the grating 111 may be set to the width of the waist of theincident optical beam. In this case, fine adjustment of the orientationof the switching substrates 100 a, 100 b and lens arrays 30, 35 can bemade by monitoring the back-reflected light in the optical fibers 22,27.

FIG. 9 illustrates an exemplary arrangement for detecting back-reflectedlight in a fiber 22. As shown in FIG. 9, fiber 22 includes a segment 22a having a first end aligned or integrated with a micro-lens 32. Asecond end of segment 22 a couples to an optical circulator 332.Circulator 332 also couples to ends of segments 22 b and 22 c. A secondend of segment 22 b couples to a light source (e.g., a light-emittingdevice, such as a laser). A second end of fiber 22 c couples to aphotodetector 334, such as a PIN diode or a metal-semiconductor-metal(MSM) photodiode. The photodetector 334 can be coupled to an amplifier336, which can couple to an analog-to-digital converter (ADC) 338 beforethe detected signal enters controller 50, for example.

In operation, light generated by the light source is coupled to thecirculator 332 by segment 22 b. Circulator 332 couples the light fromsegment 22 b to segment 22 a, which couples the light to lens 32.Back-reflected light from segment 22 a is coupled by circulator 332 tosegment 22 c. Photodetector 334 detects the back-reflected light onsegment 22 c. For example, photodetector 334 may generate an electriccurrent indicative of the power of the back-reflected light. Amplifier336 may be provided to amplify the output of photodetector 334.Amplifier 336 may be a transimpedance amplifier that generates a voltagesignal based on an input from photodetector 334. ADC 338 converts thevoltage of the amplifier 336 to a digital signal, which may be suppliedto controller 50. Based on the output of the ADC 338, the controller 50can determine whether the lens array and switching substrate 100 areproperly aligned. For example, the controller 50 may determine that thesubstrate and lens array are properly aligned if a predetermined powerlevel (e.g., a maximum power level) of back reflected light is detectedin each fiber 22. Alternatively, the output of the photodetector 334,the amplifier 336, or the ADC 338 may be provided to a meter or otherdisplay that can be read by technicians while aligning the fiber/lensarray and switching substrate.

FIG. 10 illustrates another exemplary arrangement for detecting backreflected light in a fiber 22. In accordance with FIG. 10, fiber segment22 a includes a first end aligned or integrated with a micro-lens 32 anda second end aligned or integrated with a lens 331 a. Fiber segment 22 bincludes a first end coupled to a light source (not shown) and a secondend aligned or integrated with a lens 331 b. A beam splitter 333 isprovided between lens 331 a and lens 331 b. A lens 331 c is alsoprovided in alignment with beam splitter 333. Lens 331 c maybe alignedor integrated with fiber segment 22 c. The remainder of the detectorarrangement may be the same or similar to that described in connectionwith FIG. 9.

In operation, light generated by the light source is coupled to the lens331 b by segment 22 b. The light passes through the beam splitter 333and is inserted into segment 22 a by lens 331 a. Segment 22 a couplesthe light to a lens 32 of lens array. Back-reflected light from segment22 a is coupled to beam splitter 333 through lens 331 b. The beamsplitter 333 reflects the back reflected light into segment 22 c throughlens 331 c. Photodetector 334 detects the back reflected light. A signalindicative of the back reflected light may be supplied to controller 50.Based on the output of the signal, the controller 50 can determinewhether the lens array and switching substrate 100 are properly aligned.

The detector arrangements of FIGS. 9 and 10 are intended to beillustrative. Of course, other mechanisms may be provided for detectingthe back reflected light.

The alignment features of the present invention have been describedprimarily in connection with an optical switch having reflectiveswitching elements. However, the alignment features and techniquesdescribed herein are applicable to the alignment of a fiber/lens arrayand other optical switching components, such as those used in liquidcrystal optical switches and other types of optical switches thatutilize free-space optics, to name just a few. Moreover, while thepresent invention has been described in connection with optical switchcomponents, it should be appreciated that the alignment mechanismsdescribed herein may be used to align various types of equipment. Thealignment mechanisms may be used together with other alignmentmechanisms. For example, the alignment mechanisms described herein maybe used for fine positional adjustments while other mechanisms may beused for coarse adjustment.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thescope or spirit of the invention. Other embodiments of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. It isintended that the specification and examples be considered as exemplaryonly, with a true scope and spirit of the invention being indicated bythe following claims.

What is claimed is:
 1. An optical switch comprising: a fiber/lens arrayincluding a plurality of input optical fibers carrying a plurality ofinput optical signals and a plurality of micro-lenses; a plurality ofoutput optical fibers; and an optical switching mechanism forselectively coupling input optical signals from said plurality of inputoptical fibers to said plurality of output optical fibers, said opticalswitching mechanism including a switching substrate having a side facingsaid fiber lens array, the side having at least one alignment gratingand a plurality of switching elements aligned with the micro-lenses,wherein the alignment grating is positioned to reflect an optical signalpassing through at least one of the micro-lenses.
 2. The optical switchaccording to claim 1, wherein said switching elements comprise movablemicro-mirrors.
 3. The optical switch according to claim 1, wherein saidswitching substrate and said fiber/lens array are oriented with respectto each other such that optical signals from the fiber/lens array areincident relative to the surface of the switching substrate at an angleα.
 4. The optical switch according to claim 3, further comprising anoptical detector for detecting a back-reflected optical signal in atleast one of the plurality of input optical fibers, wherein theback-reflected optical signal is produced by the alignment grating. 5.The optical switch according to claim 3, wherein said alignment gratingreflects a first order or higher-order component of an optical signalincident thereto at the angle α.
 6. The optical switch according toclaim 1, wherein said switching elements and the alignment grating areprovided in an array at a surface of the switching substrate.
 7. Amethod of aligning a fiber/lens array and a switching substrate of anoptical switch, wherein the fiber/lens array includes a plurality ofoptical fibers and a plurality of micro-lenses aligned with the opticalfibers and the switching substrate includes a grating and a plurality ofswitching elements, the method comprising: directing an optical signalhaving a predetermined wavelength through one of the optical fibers andthrough one of the micro-lenses in the direction of the switchingsubstrate; moving at least one of the fiber/lens array and the switchingsubstrate such that the optical signal impinges on the grating;detecting power of an optical signal reflected from the grating; andfixing the position of the fiber lens array and the switching substraterelative to each other when the detected power meets a predeterminedoptical power criterion, whereby the switching elements of the switchingsubstrate are aligned with micro-lenses of the fiber/lens array.
 8. Themethod according to claim 7, wherein the predetermined optical powercriterion comprises a maximum optical power.
 9. The method according toclaim 8, wherein the predetermined optical power criterion comprisesequaling or exceeding a threshold power value.
 10. A method of aligninga fiber/lens array and a switching substrate of an optical switch,wherein the fiber/lens array includes multiple optical fibers and amultiple micro-lenses aligned with the optical fibers and the switchingsubstrate includes a plurality of gratings and switching elements, themethod comprising: directing optical signals having a predeterminedwavelengths through a plurality of the optical fibers and through themicro-lenses in the direction of the switching substrate; moving atleast one of the fiber/lens array and the switching substrate such thatthe optical signals impinge on the gratings; and detectingback-reflected optical signals in the plurality of optical fibers,wherein the gratings back-reflect at least a portion of the opticalsignals at the desired angular orientation between the fiber/lens arrayand the switching substrate.
 11. The method according to claim 10,wherein the gratings reflect first order or higher-order components ofthe optical signals at the desired angular orientation.
 12. The methodaccording to claim 10, wherein the gratings are spaced apart on aperiphery of a surface of the switching substrate.
 13. The methodaccording to claim 10, wherein the switching substrate comprises amicro-electromechanical system (MEMS) substrate, wherein the switchingelements comprises movable micro-mirrors arranged in an array with thegratings on a surface of the substrate.
 14. A combination comprising: atleast one light source for producing light of a predeterminedwavelength; a fiber/lens array comprising optical fibers andmicro-lenses arranged in an array, a first plurality of the opticalfibers for carrying the light from the at least one light source and asecond plurality of the optical fibers for carrying optical informationsignals, each optical fiber associated with one of the micro-lenses toform a fiber/micro-lens pair; and a switching substrate having a surfacefacing the fiber/lens array, the surface including a plurality ofswitching elements and a plurality of gratings, wherein the gratings arealigned with the fiber/lens array to reflect the light from the at leastone light source to predetermined positions away from the switchingsubstrate and the switching elements are aligned with the fiberilensarray to reflect the optical information signals from the second opticalfibers.
 15. The combination according to claim 14, wherein the gratingsare designed to reflect the light to predetermined position on thefiber/lens array.
 16. The combination according to claim 14, wherein thegratings are designed to reflect light back through the lenses andfibers from which the light passed before being reflected by thegratings.
 17. The combination according to claim 16, wherein theback-reflected light comprises a first order or higher-order componentof the light incident on the gratings.
 18. A combination comprising: afiber/lens array comprising optical fibers and micro-lenses arranged inan array, each optical fiber associated with one of the micro-lenses toform a fiber/micro-lens pair; at least one light source coupled to afirst plurality of the optical fibers for producing light of apredetermined wavelength such that the light passes through the firstoptical fibers and associated micro-lenses, a second plurality of theoptical fibers for carrying optical signals; a first switching substratehaving a surface facing the fiber/lens array, the surface including aplurality of switching elements and a plurality of gratings, wherein thegratings are aligned with the fiber/lens array to reflect the light fromthe at least one light source to predetermined positions away from theswitching substrate; and a second switching substrate having a surfacefacing the first switching substrate, the surface including a pluralityof switching elements, wherein the switching elements of the firstswitching substrate are aligned with the fiber lens array to selectivelyreflect optical signals from the second, optical fibers to selectedswitching elements of the second switching substrate.
 19. Thecombination according to claim 18, wherein the predetermined positionscomprise the lenses and fibers from which the light passed throughbefore being reflected by the gratings.
 20. The combination according toclaim 19, wherein the light reflected to the predetermined positioncomprises a first order or higher-order component of the light incidenton the gratings.